Fuel control



June 2l, 1960 s, G, BEST FUEL CONTROL Filed Dao. 21,

PEOPLLEE C 0N 7 E 0L /NvENToR 0`gA/VLEV 6. BEST United States Patent OFUEL CONTROL Stanley G. Best, Manchester, Conn.,

Aircraft Corporation, ration of Delaware assigner to United Thisinvention relates to controls for turbine type power'plants and moreparticularly to combined propeller pitch and fuel controls for turboproppower plants.

It is an object of this invention to provide a control which compensatesfor` the response time lag between propeller pitch change and fuel owchange during transient conditions.

It is a further object of this invention to provide a control of thetype described which incorporates a droop type fuel control with a resetmechanism for the scheduled fuel flow so that the desired fuel flow isalways achieved for steady-state conditons while permitting thepropeller control' and fuel control to be separate and avoiding thenecessity of the two controls tracking each other.

These and other objects of this invention will become readilyapparentfrom the following detail description of the drawing which is aschematic illustration with some of the parts in cross section.

My copending patent application Serial No. 476,716, filed by Stanley G.Best, December 2l, 1954, now Patent 2,829,722, discloses a turbopropcontrol system which utilizes a common r.p.m. sensing device for boththe fuel control and the propeller pitch control to avoid trackingerrors between the two controls. This fuel control system has similardynamic properties as the one disclosed in the above-referred toapplication, however, a droop type fuel control is utilized with aresetting mechanism such that it is not necessary to have the propellerpitch control and the fuel control track each other.

Referring to the drawing, a turboprop power plant combination isgenerally indicated at and includes a compressor ,section 12, acombustion section 14 and a fturbine and exhaust section 16. As isusual, at least a portion of the turbine section drives a variable pitchpropeller 18. The propeller 18 has the pitch of its blades regulated bya control schematically illustrated at 20. The propeller control and thepitch changing mechanism may be of the type shown and described inCaldwell et al. Patent No. 2,174,717 or Martin Patent No. 2,361,954.

A single power lever 30 is operatively connected to a group ofcoordinating cams for both the propeller and fuel controls. The powerlever is adapted to rotate a governor setting cam 32, a fuel flowscheduling cam 34 and a propeller governor setting cam 36. The cam 36,`of course, will normally adjust a Speeder spring of a governor which inturn regulates the pitch of the blades of the propeller 18.

The cam 32 operates the rack 40 which by means of pinions `42 and 44drives a rack 46 through a pulley and cable arrangement 48 and 5l). Therack 46 sets a Speeder spring 52 which opposes the centrifugal forceprovided by yweights 54 which may be rotated in proportion to the speedof rotation of the power plant by any suitable well known means. Thespring 52 and the flyweights 54 comprise a governor for operating anr.p.m. pilot valve generally indicated at 56. The governing mechanismmoves the valve stem 58 and the East Hartford, Conn., a corpolands 60and 62 so as to conduct high pressure Huid or drain pressure to thechamber 66 of an r.p.m. servo device generally indicated at 68. Ther.p.m. servo has a piston 70 portions of which are of different areas.High pressure fluid is continuously supplied to the chamber 72 so thatwhen high pressure fluid is conducted to chamber 66 the piston 70 movesdownwardly, while if drain pressure is supplied to the chamber 66 thepiston 70 is moved upwardly. Thus it will be seen that the fuel droopgovernor, in response to either a power lever movement or a speedchange, positions the r.p.m. servo 68 via the r.p.m. pilot valve 56which in turn moves the rod 76 and varies the opening of the fuel valve78 in a manner to be described hereinafter. The r.p.m. servol piston viathe rod 76 and beam 80 also moves a followup sleeve 82 which surroundsthe lands 60, 62 of the r.p.m. pilot valve' 56. As -a result theposition of the r.p.m. servo piston 70 always essentially corresponds tothat of the pilot valve stem 58, including the lands 60 and 62. lhisprovides the desired fuel flow droop.

Fuel flow droop can be described as a deviation of the iinal fuel flowvalue from the desired (set) fuel flow over the full operating range.Thus, when an olf conv dition occurs, the fuel flow does not eventuallyreturn to the exact same set conditon. This slight error or deviationprovides a certain amount of stability to the control. The output of ther.p.m. servo 68, namely the motion imparted to rod 76, also moves areset pilot valve 86 via the arm 88. In addition, the power lever canalso move the reset pilot valve via the cam 34 and the` rod 90. Thereset pilot valve 86 includes aland 94 which can pass high pressure uidor fluid under drain pressure via the line 96 to the chamber 98 of areset servo 180. The reset pilot valve meters fluid into or out of thechamber 98 of the reset servo 100 so that it moves at a rateproportional to the reset pilot valve displacement. A restriction 102may be provided in the line 96 so that the reset servo has a relativelyslow response. With the reset servo having a slow response and ther.p.m. servo 68 having a relativelygrapid response the control reactssuch that during dynamic transients the action is similarV to that of apermanent` droop governor control, giving good stability and high rateof response,'

the resetbeing sufficiently gradual to have little effect on response.

The reset servo 100 by means of a reset spring 162 adds or subtractsspring force to the droop governor thus changing its setting. Thischange in setting in turn causes the stem 58 of the r.p.m. pilot valveS6 to move thereby in turn causing motion of the piston 70 of the r.p.m.servo 68 until it has in turn recentered the land 94 of the reset pilotvalve 86. The reset pilot valve being an integrating type of device willalways return to its centered positon insuring that the steady-rate fuelflow is always that value which has been scheduled by the setting of thecam 34 and rod 90.

The action of the speed responsive mechanism is first to correct fuelflow in a direction to correct for an off speed condition and then tobegin to reset itself in a direction to restore the fuel valve in itsoriginal position regardless of speed change. The propeller governor isfinally relied upon to bring the engine back to on speed. The resetaction is in a sense to restore the original fuel valve position and isa floating action` which can only reach a null when the end of link 88is in such a position so as to close the pilot 86, and this position isfixed relative to the position of the fuel valve for any givencompressor inlet pressure.

The action of the r.p.m. servo 68 on the throttle valve 78 is modifiedby the motion of a bellows 110 and rod 112. The bellows 110 is sealedand the outside thereof is exposed to compressor inlet pressure andtemperature y such that the bellows responds to both inlet pressure andtemperature. Motion of the free end of the bellows 110 and rod 112positions a roller 114 which is interposed between the throttle valvestem 116 and a lever 118 which is engaged by the rod 76. vThe lever '118is pivoted at 120;:

The pump feeding fuel to the throttle valve normally would have theoutlet pressure thereof maintained constant; or, the pressure drop-across the throttle valve may be maintained constant by means of aby-pass type regulator 13G-so that for any given position of thcthrottle valve a predetermined fuel ow will be obtained. These arewell-known expedients in the art.

With a fuel control system of the type described, control functions ofthe following nature are obtained.

During transient conditions fuel ow is altered from the equilibrium orsteady state value in a manner to aid in rapidly bringing the engine tothe selected speed in a we ll damped'manner, while equilibrium or steadystate fuel ow is accurately defined, independent of any tracking errorsbetween fuel and propeller control settings.

As a result of this invention it is readily apparent that a relativelysimpleyet highly accurate but dynamically stable control is provided.

Although only one embodiment of this invention has been illustrated anddescribed herein, it will be apparent that various changes andmodifications may be made in the construction and arrangement of thevarious parts without departing from the scope of this novel concept.

What it is desired to obtain by Letters Patent is:

1. In a fuel control for a turbine type power plant, a source of fuelunder pressure, means for regulating the ow of fuel from said source tothe power plant, manual means for setting said means for regulating theow of fuel to maintain a desired fuel flow rate, a speed governorresponsive to the speed of the power plant, means for setting Asaidgovernor including an adjustable spring, a pilot valve biased in onedirection by said spring and in the other direction by centrifugalforce, a servo device controlled by said pilot valve and operativelyconnected to said'fuel regulating means for tem,- porarily varying fuelow upon a change in power plant speed from the set speed, mechanismresponsive to the relative position of said servo device and saidmanuall means for resetting said governor including a second adinstablespring biasing said pilot valve in opposition to said first-mentionedspring said mechanism returning said fuel flow regulating means to itsoriginal position, and means responsive to at least one parameter ofpower plant operation for further varying fuel ow.

2. In a turboprop power plant including a propeller having variablepitch blades, means for regulating the pitch of said bladesvto increasethe load on the engine with an increase inu speed and to decrease theload on the engine with a decrease in speed, a droop fuel governor, afuel ow scheduling member, power control means for controlling saidpitch regulating means and setting said governor and said fuel owscheduling member, said governor including -a pilot valve, a fuelcontrol valve for regulating the flow of fuel to the power plant, aservo device controlled by said pilot valve for varying the position ofsaid fuel valve with variations in speed, a follow-up sleeve surroundingsaid pilot valve and operatively connected to said servo device to varythe effect of said pilot valve on said servo device, means for resettingsaid governor including a second servo device, a reset pilot valve forcontrolling said second servo device including operative connections tosaid first servo chamber, a turbine driven by device and said fuel flowscheduling member for comparing the relative positions thereof to returnsaid fuel control valve to its original set position after a transientspeed change, and means responsive to at least one parameter of powerplant operation for further regulating the ow of fuel by said fuelcontrol valve.

3. A turbine type power plant including a combustion the'v gases fromsaid combustion chamber, a compressor driven by the turbine, a variablepitch propeller driven by the power plant, means for varying thc pitchof the propeller to control the speed of rotation thereof, a sourceoffuel under pressure,

' means for regulating the flow of fuel from said source to saidcombustion chamber, power control means for manually setting a scheduleof fuel ow and operatively connected to said regulating means, a speedgovernor including a pilot valve, means for setting the speed of saidgovernor in accordance with the setting of said power control means, afirst servo device controlled by said pilot valve for changing the fuelflow regulated by said fuel regulating means when said speed governorcalls for a fuel iiow different than that called for by said powercontrol means, a follow-up sleeve for said pilot valve, follow-up meansmechanically connecting said first servo device and said Sleeve, a resetservo device connected to said power control means and said first servofor rey setting said governor to eventually return said fuel regulatingmeans to the original fuel ow scheduled by saidpower control meansincluding a reset pilot valve for sensing the relative positions of saidfirst servo device and said power control means.

4. A power plant including a combustion chamber, a variable load forsaid power plant, means for controlling the Speed of the power plantduring variations inload, sa source of fuel under pressure, means forregulating the ow of fuel from said source to said combustion chamber,power control means for setting a schedule of fuel flow and operativelyconnected to said regulating means, a speed governor driven bythe'engine. means for setting the speed of said governor in accordancewith the setting of .said power control means, a first servo devicecontrolled by said governor for changing the fuel iiow regulated by saidfuel regulating means when said speed governor is in an off-speedcondition calling for a fuel iiow different than that called for by saidpower control means, follow-up means mechanically connecting said firstservo device and said governor, and a reset servo device connected tosaid power control means and said first servo device for comparing therelative positions of said control means and first servo for resettingsaid governor to eventually return said fuel regulating means to theoriginal fuel ow scheduled by said power control means, said means forcontrolling the speed of said power plant being effective to eventuallyreturn the power plant to the set speed when an off speed occurs.

References Cited in the le of thispatent UNITED STATES PATENTS

